Powertrain mounting systems used in motor vehicle applications include the “pendular” mounting system, exemplified at FIG. 1. In the pendular mounting system 10, there is included (dispositions being relative to forward travel direction 26 of the motor vehicle) a right-hand load bearing mount 12, a left-hand load bearing mount 14, and a (rear disposed) torque reacting strut mount 18, composed of a torque strut 20 and a torque strut bracket assembly 22. The two load bearing mounts being disposed in alignment with the torque roll axis 16 of the powertrain, which passes through its center of gravity, and the torque reacting torque strut mount 18 is disposed so as to carry minimal static force pre-loading, while providing reaction to powertrain pitch arising from torque loading about the torque roll axis, wherein the pitch of the powertrain is registered at the torque strut mount component(s) generally as a couple or moment in a plane normal to the torque roll axis.
In further detail, as shown at FIGS. 2 and 3, the prior art torque reacting strut mount 18 features the torque strut 20 mounted to the cradle or other vehicle structural member 24 and the torque strut bracket assembly 22 is mounted to the power train 28 (shown in phantom at FIG. 1). The torque strut bracket assembly 22 is pivotally connected to the torque strut 20. A rigid bushing 30 of the torque strut bracket assembly carries a sleeve 32 set in rubber 34. A bolt 38 is threadingly secured to a threaded feature 60 of a torque strut clevis 36 to thereby attach the torque strut 20 to the torque strut bracket assembly 22.
As shown best at FIG. 3, the torque strut 20 includes a cylindrical head 40 connected with the clevis 36. The head 40 has a circular inner space 42 defined by an inner head race 44. Disposed in the inner space 42 is a rubber element 46 having a central body 48 and distal arms 50 which radially connect to the inner head race 44. A metallic core 52 is in part overmolded by the rubber element 46, and has a through hole 54. As shown at FIG. 2, a bolt 56 secures the torque strut 20 to the cradle or other structural member 24 via passage through the through hole 54. Powertrain pitching torque loads act on the torque strut, wherein the rubber element reacts in elastic deformation depending on the mutually opposite directions of the pitching torque loads.
When the motor vehicle is in operation, powertrain pitching due to various levels of torque loading occurs at the torque reacting mount component member(s), which includes both high and low vibration amplitudes for which damping and stiffness requisites vary. High vibration amplitude events include engine start/stop, garage shifts, rough road shake, and smooth road chuggle. Low amplitude vibration events include idle vibration and smooth road shake vibration. Therefore, a drawback of prior art torque reacting mount components utilizing solely an elastic element for reaction to powertrain pitch, is that the elastic element is unable to adjust itself in terms of stiffness and damping to the various high and low vibration amplitudes presented to it during powertrain pitching events. A secondary bumper 55 is provided for providing an abutment to the inner head race 44 in the event of an extreme engine pitch event.
A dual aspect mount device known in the prior art is a hydraulic mount used for left and right load bearing powertrain mounts. In a first aspect, a hydraulic mount provides location of one object, such as a motor vehicle powertrain, with respect to a second object, as for example the body, frame structure or cradle of the motor vehicle. In a second aspect, the hydraulic mount provides damping for high vibration amplitude events while providing low dynamic stiffness to isolate small amplitude powertrain vibration with respect to body of the motor vehicle. Hydraulic mounts which are used for motor vehicle applications are represented, for example, by U.S. Pat. Nos. 4,828,234, 5,215,293 and 7,025,341.
U.S. Pat. No. 5,215,293, by way of example, discloses a hydraulic mount having a rigid upper member which is bolted to the powertrain and a lower powertrain member which is bolted to the frame (or cradle), wherein the upper and lower members are resiliently interconnected. The upper member is connected to a resilient main rubber element. Vibration of the main rubber element in response to engine vibration is transmitted to an adjoining upper fluid chamber. The upper fluid chamber adjoins a rigid top plate having an idle inertia track there through which communicates with an idle fluid chamber. The idle fluid chamber is separated from an idle air chamber by an idle diaphragm. The idle air chamber is selectively connected to atmosphere or to engine vacuum in order to selectively evacuate the idle air chamber in which case the idle diaphragm is immobilized. A bounce inertia track is formed in the top plate and communicates with a lower fluid chamber which is fluid filled. A bellows separates the lower fluid chamber from a lower air chamber which is vented to the atmosphere.
The idle inertia track has a larger cross-sectional area and a shorter length than that of the bounce inertia track, such that the ratio provides resonant frequency damping at the respectively selected resonance frequencies. In this regard, the resonance frequency of the fluid flowing through the idle inertia track is set to be higher than that of the fluid flowing through the bounce inertia track. As such, this prior art hydraulic mount is able to effectively damp relatively low frequency vibrations over a lower frequency range, such as powertrain shake or bounce, based on resonance of a mass of the fluid in the bounce inertia track, while, on the other hand, the idle inertia track is tuned so that the hydraulic mount exhibits a sufficiently reduced dynamic stiffness with respect to relatively high-frequency vibrations over a higher frequency range, such as engine idling vibrations, based on the resonance of a mass of the fluid in the idle inertia track.
In operation, vibrations in the higher frequency range are isolated by operation of the induced fluid oscillations in the upper fluid chamber passing through the idle inertia track and the resilient deformation of the main resilient element and the idle diaphragm in that the idle air chamber is at atmospheric pressure. For vibrations in the lower frequency range, the idle air chamber is evacuated by being connected to engine vacuum, wherein now the fluid oscillations of the upper fluid chamber travel through the bounce inertia track and are damped thereby in combination with the resilient deformation of the main resilient element and the bellows.
Hydraulic mounts are employed as load bearing mounts or as a combination load bearing and torque reacting mounts. In torque roll axis mounting systems, like the pendular system, the torque reacting elements in the system are predisposed to carry minimal static preload and to primarily react to powertrain torque. In particular, bushing style mounts as the torque reacting elements in pendular systems provide specific benefits to the powertrain mounting system overall isolation not offered by other types of hydraulic mounts.
Parent U.S. patent application Ser. No. 12/904,350, filed on Oct. 14, 2010, to Gannon et al, entitled “Mounting Systems for Transverse Front Wheel Drive Powertrains with Decoupled Pitch Damping”, the entire disclosure of which is hereby incorporated herein by reference, describes a motor vehicle powertrain mounting system including a hydraulic device torque reacting component member flexibly interconnecting first and second torque reacting mount components. The present invention provides structural implementation of a hydraulic device as an integral component of a torque strut.